The CIA ran a secret program for nearly eight years that aspired to kill top al-Qaeda leaders with specially trained assassins, but the agency declined to tell Congress because the initiative never came close to bringing Osama bin Laden and his deputies into U.S. cross hairs, U.S. intelligence and congressional officials said yesterday.

The plan to deploy teams of assassins to kill senior terrorists was legally authorized by the administration of George W. Bush, but it never became fully operational, according to sources briefed on the matter. The sources confirmed that then-Vice President Richard B. Cheney had urged the CIA to delay notifying Congress about the diplomatically sensitive plan -- a bid for secrecy that congressional Democrats now say thwarted proper oversight.

The program, which was terminated last month, touched off a political firestorm last week when several Democrats said the CIA had misled Congress by not disclosing its existence. CIA Director Leon E. Panetta gave lawmakers their first overview on June 24, within hours of learning about it, the officials said.

Some officials familiar with the program said certain elements of it were operational and should have been disclosed because they involved "significant resources and high risk," as one intelligence official described it. But others said the initiative never advanced beyond concepts and feasibility studies.

Intelligence officials also offered conflicting views of Cheney's alleged role. One official recalled that the vice president ordered only a temporary delay in notifying Congress, until the planning for an al-Qaeda hit crossed certain thresholds -- for example, a planned movement of operatives across international boundaries. "What is being labeled now as covert action never reached that point," said the official, who is familiar with intelligence committee briefings on the matter.

Three former intelligence officials who were close to the program said it operated within legal guidelines.

"Everything we did fell under the [authorizations] of both administrations, Democratic and Republican," said one former counterterrorism official with detailed knowledge of the program. "We would have been professionally negligent if we had not taken the actions we did. There was zero legal risk in my mind."

Panetta's revelation that he had terminated the program drew fresh criticism from Republican lawmakers yesterday.

Neither the officials nor the CIA would elaborate on the program or explain how it differed from other, well-understood attempts to destroy al-Qaeda's senior leadership. But one U.S. intelligence official, speaking on the condition of anonymity, said the program was small and intermittent and "exactly the kind of work people would expect the agency to be doing."

The CIA was authorized in 2001 to use lethal force against a small group of top al-Qaeda leaders. Although the agency's attacks on terrorist camps using pilotless aircraft is well documented, the newly disclosed program involved operatives "striking at two feet instead of 10,000 feet," an intelligence official said.

Senior White House officials said President Obama was briefed on Panetta's decision after returning to Washington early Sunday from an overseas trip. The officials said the White House was not consulted before Panetta canceled the program. They declined to elaborate.

On Sunday, key Democrats called for an investigation of whether the CIA broke the law by not briefing Congress. The claims of inappropriate secrecy also fueled calls for the Obama administration to begin a formal investigation of the CIA's counterterrorism policies during the Bush administration.

Some details about the CIA's newly disclosed program were first described in an article on the Wall Street Journal's Web site Sunday night. Yesterday, former and current intelligence officials characterized the initiative as a series of discrete attempts to locate and kill bin Laden and his top deputies as new leads surfaced about their possible whereabouts. Bin Laden is believed to be living in a rugged area along the Afghanistan-Pakistan border.

U.S. officials have said they think bin Laden is in Pakistan, so any attempt to kill him using ground forces probably would require an incursion into Pakistani territory.

One current intelligence official said the program was always small, but over time the agency considered different approaches that took advantage of evolving technical capabilities. Options were being actively weighed as recently as this spring, said the official, who added that Panetta learned of the program during a briefing that described new CIA proposals for going after bin Laden.